End of Season Report V2 from the Boilertron 3000

fentonc

Last year was the first time I tried instrumenting my boiler - I'm back again this year! The code is pretty reliable (and a little more accurate), and the big change was moving the 2nd floor thermostat sensor from the master bedroom to the small bedroom. I'm happy to report the honeywell redlink thermostat was simple to setup and has been operating trouble-free all season, and significantly increased bedroom comfort for all parties involved. Thanks to those who suggested it!

Now, the stats!

• 3895 Heating Degree Days (vs 65F)
  
• Burned a total of 325 Therms of gas
  
• Average boiler efficiency: 46% (sigh)
  
• Average Fuel BTU/HDD65-hr: 347
  
• Coldest average daily temp: 12F (53 HDD65 - right at our local design temp!)
  
• 1701 total boiler cycles
  
• 7340 total burn cycles
  

And now in charts and graphs:









You can very clearly see the effective of setbacks - both the 1st and 2nd floors kick on at 6:45am and turn off at like 8:30am, temporarily raising the thermostat setpoint from 62 to 68. Frequently the 1st floor took long enough to heat up that it's calling for heat that entire time.

My summer project is to try to build a PLC-thing to do some kind of zone synchronization (and temporarily pause the circulator while closing zone valves to avoid that annoying 'ka-thunk' sound when one zone shuts off while another is running). Remember kids - do a proper heat loss calculation before replacing a boiler!

EdTheHeaterMan

1701 total boiler cycles
7340 total burn cycles

That is an average of 4.5 cycles per call for heat.
and the 90 second run time tell me that your radiators can't handle the output of the boiler so the burner goes off via the high limit in pretty short order.

Now you have verified that your boiler is grossly oversized for the connected radiation. But you already knew that.

Thanks for the report!

fentonc

Yes, but now I know how much it's oversized to 3 decimal places At some point I should probably learn how to solder pipes instead of just wires, but it's at least been interesting to go down the rabbit hole learning about all this stuff.

hot_rod

That 7300 number is huge, and has much to do with that low efficiency number. Seems like a piping fix, add a buffer perhaps, would have a reasonable payback?

Steamhead

This is quite interesting.

Question- obviously the boiler is oversized. How does the boiler's output compare to the house's heat-loss calculation?

fentonc

@Steamhead - the boiler is a Weil-Mclain Gold CGa-PIDN-5 with a nominal input of 140,000 BTU/h, but I've clocked it at the gas meter and it's reliably 120,000 BTU/h (my understanding is that the boiler has an input gas valve that is probably too closed). My setup measures the supply/return water temperatures while the zone valves are open and, based on the datasheets and linear footage of baseboards, it checks every ~1 second and tracks the estimated delivered heat to each zone. Based on that, on the coldest day of the year (which was conveniently exactly at the design temp of 12F), it delivered about 20,400 BTU/hr. Presumably some of the jacket losses from the boiler actually winds up in the finished space (although it's surrounded by uninsulated concrete block walls and concrete floor), but I don't have a good way to measure that.

@hot_rod - I don't have a good place to locate a buffer tank, although it would certainly help if I did. One of my summer projects is to build a microcontroller/relay/PLC 'thing' to sit in between the thermostats and TT switch going to the boiler to provide some amount of zone synchronization. I got a little bit of that by synchronizing the setback times on my thermostats, but I'm thinking of trying a more elaborate control scheme that forces the zones to wait until they all fire at some regular interval. I'm hopeful I can at least make it a little better without sacrificing comfort too much. An ideal solution would either be a way smaller CI boiler + buffer tank, or a modcon that can dial way down (I think some can go down to like 8KBTU/hr, but I only had 6 days this heating season with an average demand greater than 8 kbtu/hr!).

My circulator is pumping into my expansion tank, which bothers me but doesn't seem to have a huge affect on performance, but otherwise I think things are piped in a relatively sane way - the boiler is just way bigger than me heat loss, zoned or unzoned.

Steamhead

OK, that's probably a CGa-5 Series 2. The manual and ratings are here:

https://www.weil-mclain.com/sites/default/files/field-file/CGa Series 2 Boiler Manual - date code 12-2012.pdf

The current CGa-5 Series 3 has a slightly lower rating.

It would still be interesting to know each zone's calculated heat loss, to see how that compares with the system's behavior.

109A_5

Hello @fentonc,

"3895 Heating Degree Days (vs 65F)"

Days or Hours ?
3895 Days ends up being a lot of years.

fentonc

@109A_5 - "Heating Degree Days" (HDD) is correct. One day with an average temperature of 30F is considered "35 heating degree days" vs the indoor temperature of 65F.

@Steamhead - On my coldest day of the season I logged the following per-zone delivered BTUs:

• Basement: 4290 BTU/hr
  
• 1st floor (lots of windows and doors): 9950 BTU/hr
  
• 2nd flooor: 6160 BTU/hr
  
• Total: 20,400 BTU/hr
  

I also tried using the Slant/fin app to do a heat loss calculation and got the following estimates:

• Basement: 10,500 BTU/hr
  
• 1st floor: 12,500 BTU/hr
  
• 2nd floor: 11,250 BTU/hr
  

I suspect that at least some of the boiler jacket losses turn into useful heat in the basement (so my measured number is probably low), and some of the 1st floor heat moves to the 2nd floor via rising air, but overall there is reasonable agreement. The 1st floor generally has poor air sealing around all of the windows/doors, and has a lot more of those compared to the basement and 2nd floor. The baseboard was just installed around the perimeter where possible (plus a few inner locations in the 1st floor), so has little relationship with the actual heat loss.

109A_5

Ok, thanks, I looked it up, I understand now.

fentonc

@hot_rod - here is a pic of the near boiler piping:


Aside from the circulator pumping into the expansion tank, there's not really anything wrong with the near boiler piping, is there? The very low delta-T values I see seem to indicate the flow rate is just fine. I think it's just a fundamental mismatch between the huge boiler output and the inability to sink that heat when only 1 zone is calling (and my relatively low heat loss). That's why I'm hoping synchronizing the zones might improve things at least a little bit, as I see much longer burn times ( a couple of minutes, at least, instead of 80 or so seconds) if all three zones are open.

Dave Carpentier

No way to hang something like a 20 gallon buffer from the ceiling ?

hot_rod

fentonc said:

@hot_rod - here is a pic of the near boiler piping:


Aside from the circulator pumping into the expansion tank, there's not really anything wrong with the near boiler piping, is there? The very low delta-T values I see seem to indicate the flow rate is just fine. I think it's just a fundamental mismatch between the huge boiler output and the inability to sink that heat when only 1 zone is calling (and my relatively low heat loss). That's why I'm hoping synchronizing the zones might improve things at least a little bit, as I see much longer burn times ( a couple of minutes, at least, instead of 80 or so seconds) if all three zones are open.

Tight space, no doubt. I hate to see leak prone devices like backflow preventers and expansion tanks over the boiler jacket.

No air purger?

As long as the zone sync doesn't screw with your comfort, give it a try. We like the zone-ability of hydronics
The boiler is over-sized, no way around it.

Time, effort and $$ to install a buffer, would it be worth it?